1. Field of the Invention
The present invention relates to a process of driving large, open end piles in the ocean floor. It also relates to apparatus for carrying out this process.
Geologists believe that the outer continental shelf and the continental slope will be the next major areas for oil and gas exploration. Organics have been raining down for millions of years, and the tectonic activity along the interface between the oceanic and continental crustal plates has provided continuous heat for distillation.
In the areas of the outer continental shelf and the continental slope, the water is considerably deeper than it is in the areas of the ocean where the oil and natural gas industry currently drills. In this deeper water, almost all offshore surface structures must float. With a few exceptions, they will not stand on fixed foundations. These floating structures will require reliable moorings to maintain their stations during severe weather. Failure to maintain station can result in loss of time and equipment and jeopardize both personnel and environment. An uncontrolled oil well left behind on the ocean floor would be an environmental disaster. Thus, in the near future, the offshore industry will need a new generation of reliable high capacity deep water moorings.
In deep water, an exploratory well can be drilled from a dynamically positioned ship. However, to complete and produce from such wells in these deep waters, a template must be installed on the ocean floor to secure the well head equipment and anchor the tension leg platform floating above. These templates require piles that have large capacities in tension in addition to their compression capacity. There is also a need in deep water for individual high capacity anchor piles where there is anything, permanent or temporary, floating above that must maintain its station.
Outer continental shelf and continental slope soils can vary, but most of these deep water deposits are soft and unconsolidated near the ocean floor. The simplest way to develop substantial holding power in these deep water soils is with the outside skin friction of piling which have significant penetration.
Using existing anchorage methods, it is anticipated that the cost of installing the anchorage system for a deep water offshore structure will be approximately 25 percent of the total in place cost of the structure. As the water depth increases, so does this percentage. As an alternative to these escalating costs, the new pile driving system presented herein provides a way to install a versitile, economical and dependable high capacity deep water anchorage system.
2. Description of the Prior Art
Large embedment anchors and dead weights are very expensive to install in deep water. They are also untrustworthy in soft soils, on slopes and in earthquake zones. Dead weights slide on the ocean floor; embedment anchors offer little resistance to non-horizontal loads; and long catenary anchor moorings are depth limited. Any anchorage system that does not significantly penetrate the ocean floor in areas of potential turbidity currents such as the continental slope, could instantly disappear.
Proposals have been made for underwater pile driving systems that include hydraulic hammers with power packs mated to the pile and jacking systems which attach themselves to a template. These remote control devices appear feasible. However, they would have to be gigantic to drive a large pile to a significant penetration depth in deep water. Hammers are depth limited and hydraulic jacking devices must jack against something.
The following is a description of certain U.S. patents, in numerical order, which disclose prior art technology.
U.S. Pat. No. 2,994,202 discloses a hydraulic jack. Hydraulic pressure is used to control the relative position of the earth penetrating member (column 1, lines 28-31). The lower end of the caisson is provided with a flushing line 58 (column 2, lines 40-43).
U.S. Pat. No. 3,263,641 discloses a suction plate. It comprises an open bottom compartment in selective communication with one or more closed fluid-tight compartments. A description of the use of the suction plate is provided beginning at column 2, line 71, and continuing through column 3, line 21.
U.S. Pat. No. 3,380,256 discloses an underwater drilling installation that is basically a drilling rig in a large tube. As shown in FIG. 7, seawater may be pumped from the interior of the tube after it has been lowered to the ocean floor.
U.S. Pat. No. 3,431,879 discloses an anchor box. Basically, the empty anchor box is transported to the location where it will function as an anchor, and then material from the ocean floor is pumped into the interior of the anchor to increase its weight.
U.S. Pat. No. 3,496,900 discloses a method for installing a deep water anchor. FIG. 3 includes a diagramantic illustration of the steps of one embodiment of the method. Tubular member 20 is provided with a concrete cap 24 and an open lower end 21 (column 3, lines 28-35 and 42-44). Cavity 25 in tubular member 20 is filled with seawater and lowered to the ocean floor (column 5, lines 1-10). Upon contact with the ocean floor, peripheral lip 15 penetrates the ocean floor thereby establishing a partial seal, and displacing a portion of the water in cavity 25 through pipe 36 (column 5, lines 11-26). The seawater and flowable mud in cavity 25 are removed by tube 36, line 40 and a pumping system. The hydrostatic force will push the anchor into the ocean floor (column 5, lines 27-35). It is noted that the anchor may be removed and salvaged (column 5, lines 60 through column 6, line 30).
U.S. Pat. No. 3,721,095 discloses a system for controlling the magnitude of a driving force being exerted on a substantially rigid object being driven into the earth, such as a pile. One aspect of this method involves providing a regulated feeding of pressurized fluid into a bounce chamber beneath a massive piston weight to cause the piston weight to bounce up and down (column 2, lines 34-38).
U.S. Pat. No. 3,805,534 discloses a slide resistant platform anchor conductor silo. Anchor 10 is provided with removable end closure 7, which is removed prior to the positioning of anchor 10 over the final location (column 2, lines 52-54). It is noted that reduction of the pressure inside anchor 10 below the hydrostatic head above the anchor 10 provides a penetrating force (column 2, lines 57-59).
U.S. Pat. No. 3,817,040 discloses a pile driving method. Tubular steel piling 1 is provided with piston 13. With reference to FIGS. 1a-1d, the piston 13 is initially positioned adjacent to the lower end of the piling 1. The piling 1 is placed on the ocean floor G. A high pressure jet of water is then directed through valve 9, jet-pipe 7 and nozzle 8 against the ground underlying the piling. As the water from this jet of water fills the lower portion of the piling 1, piston 13 is lifted upward (column 2, lines 31-40).
U.S. Pat. No. 3,820,346 discloses a free piston water hammer pile driving method. The free piston provides the pile driving action. The figures of the drawings illustrate pistons 10, 44, 80U, 80L and 174.
U.S. Pat. No. 3,832,858 discloses a process of placing piles in the ground. It includes an elevatable base so that the weight of the entire pile driving rig is applied to the pile.
U.S. Pat. No. 3,928,982 discloses a method and device for a foundation by depression in an aquatic site. One of the objects of the method is to avoid the disadvantage of piles having to be driven in (column 1, lines 35-36). The tank 6 is provided submerged pumps 13 that are adapted to pump water from beneath the tank 6, through filters 14 and columns 5.
U.S. Pat. No. 4,086,866 discloses anchoring devices. The second embodiment is illustrated in FIG. 5. In operation, member 10 is lowered to the ocean floor. Fluidizing water is supplied through pipe 54 and chamber 53 to apertures 55. An air-lift pump is provided in suction passageway 12 and comprises apertures 56 which are fed with compressed air from pipe 57. The fluidizing water from aperatures 55 in combination with the suction in passageway 12 act to remove material from beneath the body of member 10 thereby causing it to bury itself (column 7, line 45 through column 8, line 21).
U.S. Pat. No. 4,098,355 discloses a gas discharge underwater hammer with a valve to keep water out of the impact chamber. Generally speaking, a massive ram is guided up and down in a vertical tube. The ram falls on an anvil which is attached to the top of the pile or other element to be driven (column 4, lines 53-61).
U.S. Pat. No. 4,257,721 discloses a system for the placement of piles into the sea floor. With reference to FIG. 1, ram 15 is raised and lowered by a hydraulic system. As ram 15 is raised, a void is created on the bottom side of diaphragm 14. This creates a hydrostatic driving force which causes the pile to move downward into the sea floor as long as the magnitude of the pressure differential does not exceed the bearing strength of the sea floor sediment (column 3, lines 3-23).
U.S. Pat. No. 4,362,439 discloses a hydrostatically powered pile driver hammer. With reference to FIG. 9, a hydrostatic force is exerted downwardly on ram F causing it to move downwardly in tubular member 14 from the position shown in FIG. 8, through the position shown in FIG. 9, until the ram impacts the anvil E as illustrated in FIG. 10. The force of this impact is transferred from the anvil E to the housing engaged pile B to drive the latter downward (column 5, lines 19-25).
In addition to the foregoing, it is noted that suction anchor piles are the subject of printed publications. In this regard, reference is made to the article entitled "Suction Anchor Piles--A Proven Alternative To Driving Or Drilling" by Denis Senpere and Gerard A. Auvergne of Single Bouy Moorings, Inc., which appears in the 1982 proceedings of the Fourteenth Annual Offshore Technology Conference at Volume 1, 4231-4300, OTC 4206, pages 483-487.
The prior art includes a number of attempts to use hydrostatic pressure as a pile driving force on the ocean floor. These prior attempts have resulted in shallow penetrations of the ocean floor for three basic reasons.
First, there is the problem of plugging. A pipe pile will plug with soil during penetration when the inside skin friction becomes equal to the end bearing resistance of the cross sectional area of the pile. A simple pipe pile normally plugs when it has been driven to a depth equal to three or four times its diameter. On land this is not a problem. The pile driver overcomes the additional end bearing resistance and continues to drive the pile. When a pipe pile being driven hydrostatically on the ocean floor plugs, it will act like a tube closed at both ends and penetration stops.
Second, there is the problem of piping. To drive a pipe pile hydrostatically, you must lower its internal pressure. Piping is the rapid movement of soil and water from an area of high pressure on the ocean floor outside of the pipe pile to an area of lower pressure inside of the pipe pile. When piping occurs, soil and water enter the lower open end of the pipe pile faster than the pile is penetrating. When the pile is full of soil, penetration will stop. The path traveled by the material involved in piping is from the ocean floor down to the lower open end of the pipe pile and into the pile. When this path is short, the soils' resistance to piping is weakest and visa-versa.
Third, there is the problem of using a water pump in extremely deep water. When a pile is driven hydrostatically, the maximum pressure that can be applied is the existing hydrostatic pressure above the pile cap. When a water pump is used to pump water out of the pile at depth, thereby developing the pressure differential across the pile cap, the maximum unit pressure that can be applied to the pile cap is the rating of the pump. In deep water this will be less than the existing hydrostatic pressure. The pump must be attached to the pipe pile and it would be far out of reach should maintenance or adjustment be required.